It is a common experience of professional painters and amateur decorators when opening a partially filled can of paint, for further painting or touch up work, to find the contents of the paint can have separated, dried out, formed a surface scum, or deteriorated to a point beyond possibility of further use. This is caused by contact with air which is left in the partially filled can or which leaks into cans that have not been adequately resealed, possibly due to dents in the can lid or can lip. The end result is that the partially filled can of paint is discarded.